A Review of Iron-Based Catalysts for Persulfate Activation to Remove PFAS in Water: Catalytic Effects of Various Iron Species, Influencing Factors and Reaction Pathways

Numerous studies highlight the potential degradation of per- and polyfluoroalkyl substances (PFAS) through advanced oxidation processes. A recent focus involves an innovative technology utilizing iron-based catalysts activated by persulfate, renowned for its exceptional PFAS removal efficiency. However, existing literature lacks a thorough comparison of various iron species catalyzing persulfate for PFAS oxidation, with limited analysis of key degradation factors. This paper conducts a comprehensive review, analyzing PFAS degradation efficiency, mechanisms, and pathways using persulfate activated by ferrous ions, zero-valent iron/nano zero-valent iron, iron-based multimetallic catalysts, and various supported iron catalysts. The influence of solution pH and Fe2+ concentration on the degradation process is also explored. The review reveals promising PFAS removal performance, often exceeding 90%, by iron-based materials activated with persulfate. Catalysts enhance performance through synergistic elements, optimized structural design, and diverse carriers. Acidic environments favor persulfate activation for organic pollutant degradation, while appropriate Fe2+ concentrations enhance removal efficiency, with Fe3+ regeneration being the rate-determining step. Iron-based catalyst-activated persulfate follows free radical (SO center dot- 4, center dot OH, O2-center dot) and non-free radical pathways (Fe(IV), 1O2, direct electron transfer). Perfluorooctanesulfonic acid (PFOS) degradation involves desulfurization, forming the intermediate product perfluorooctanoic acid (PFOA), followed by defluorination. The critical step is removing one CF2 unit in each round, leading to complete mineralization. The paper proposes future research directions for iron-based activated persulfate in water treatment for PFAS.